Flourishing is a state of optimal mental health that has been linked to a host of benefits for the midlife adult and society, including fewer workdays lost, better immune functioning, and the lowest incidence of chronic physical conditions like high blood pressure and arthritis (Howell, Kern, & Lyubomirsky, 2007; Keyes, 2005; Lyubomirsky, King, & Diener, 2005). The benefits of flourishing, coupled with its relative infrequency (just 17% of U.S. midlife adults are flourishers; Keyes, 2002), raise the critical question, what makes them thrive? The overarching goal of the proposed research is to examine the social psychological processes through which well-being is cultivated among midlife adults. In particular, the role of positive valuation-the extent to which individuals value positive emotional experiences-is investigated in the promotion of well-being via broaden-and-build processes. The broaden-and-build theory of positive emotions states that positive emotions are evolved adaptations that serve to build lasting resources. Positive emotions broaden our attention and thinking, and over time these expansive mindsets help people to build a variety of resources, such as the ability to be resilient or ward off a cold, which ultimately contributes to well-being (Fredrickson, 1998). Positive valuation, which is an attitude that can be induced temporarily in the laboratory, or raised over time in response to an intervention, may influence how much people attend and react emotionally to positive stimuli. These differences may not only determine the amount of positive emotions experienced but also the degree to which broaden-and-build processes occur. A series of three studies-two laboratory experiments and one randomized controlled trial-test the role of positive valuation in the promotion of well-being, by targeting three Specific Aims. These aims are: (1) to test whether positive valuation causes individuals to attend more to positive stimuli; (2) to test whether positive valuation causes individuals to react more strongly-as indicated by self-report and psychophysiological measures-to positive stimuli, and consequently demonstrate more cognitive broadening; and (3) to test whether and how positive valuation leads to greater increases in resources over time, in response to a positive emotion intervention. This program of research has important implications for effective and low-cost ways to promote the psychological and physical health of midlife adults.